1. Field of the Invention
The present invention relates to a scanning probe microscope, and more particularly to a scanning probe microscope capable of selectively carrying out high-resolution measurement based on scanning operation in a fine range and low-resolution measurement based on scanning operation in a wide range, and further being easily combined with other measuring probes.
2. Description of Related Art
A scanning probe microscope (SPM) has high measurement resolution equal to a size of atoms (no more than a nanometer (nm) scale). The scanning probe microscope has been generally used for measuring a surface shape of fine objects and is further being utilized in various fields. The scanning probe microscopes are classified into a scanning tunnel microscope (STM), an atomic force microscope (AFM), and a magnetic force microscope (MFM), etc. depending on a physical amount used for detecting operation, and therefore application domains are being increased. Especially, the AFM is suitable for detecting an even shape of sample surfaces in high resolution, and is achieving satisfactory results in the fields of semiconductor devices and disks. Hereinafter, an example of an AMF will be explained.
FIG. 6 shows one example of a conventional AMF. A sample stage 101a on which a sample 102 to be observed is placed is formed in a lower section of a frame 101. The sample 102 is kept to be static and its position is not changed. A probe tip approaching mechanism (coarse movement mechanism) 103 is fixed to the upper section of the frame 101 and further an XYZ fine movement mechanism 104 is fixed to the lower side of the probe tip approaching mechanism 103.
A cantilever 105 is disposed at an upper position above the sample 102. A probe tip 106 arranged at the tip of the cantilever 105 is directed to a surface of the sample 102. When measuring the surface of the sample 102, the probe tip 106 is placed close to the sample 102 so that the atomic force can be created between the probe tip and the sample. A basic end of the cantilever 105 is fixed to the lower end of the XYZ fine movement mechanism 104. The cantilever 105 has a necessary flexibility and therefore has such a characteristic that flexual deformation is produced depending on a change of the atomic force in relation to a change of the distance between the probe tip and the sample.
The configuration shown in FIG. 6 shows a system in which the side of the cantilever 105 is movable. The probe tip approaching mechanism 103 causes the probe tip 106 to approach the sample 102 quickly before carrying out the measurement and thus is used for the movement of a comparatively larger distance (coarse movement). The XYZ fine movement mechanism 104 is a tripod type fine movement mechanism or a tube type fine movement mechanism, which is configured by utilizing piezoelectric elements. The tripod type fine movement mechanism is provided with X, Y and Z actuators for producing a fine movement in X, Y and Z directions respectively. In case of using the tripod type fine movement mechanism as the XYZ fine movement mechanism 104, when carrying out the measurement, the X and Y actuators included in the XYZ fine movement mechanism 104 cause the cantilever 105 to scan the sample surface, while the Z actuator included in the mechanism 104 adjusts the distance between the probe tip 106 and the sample 102.
A displacement detector 107 is arranged for detecting displacement of the cantilever 105. As the displacement detector 107, an optical-lever-type detection optical system or a detector utilizing an interference method is used, for example. The optical-lever-type detection optical system comprises a laser source for emitting a laser beam and a photodetector for receiving the laser beam emitted from the laser source. The laser beam emitted from the laser source is reflected on a rear surface of the cantilever and afterward is incident on the photodetector. The incident position of the laser beam on the photodetector changes in response to the amount of the flexural deformation of the cantilever, the change as to the distance between the probe tip and the sample can be detected on the incident position of the laser beam in the photodetector.
When the operation of the probe tip approaching mechanism 103 causes the probe tip 106 to approach the sample at a fine distance of about 1 nm, the atomic force generated between the probe tip and the sample acts the cantilever 105 to produce the flexural deformation. The displacement detector 107 detects a flexural angle in the cantilever 105. A detecting signal outputted from the displacement detector 107 is inputted into an adder 108. The adder 108 compares the detecting signal with a standard value V.sub.ref and outputs a difference (deviation) signal Vd between the detecting signal and the standard value. The difference signal Vd is inputted into a control section 109. This control section 109 generally carries out proportional and integral compensation (PI control) and an output signal (Vz) from the control section 109 is supplied to the Z actuator of the XYZ fine movement mechanism 104 so as to change the distance between the probe tip 106 and the sample 102 to become a set value. The distance between the probe tip 106 and the sample 102 is always kept to be a predetermined constant distance based on the standard value V.sub.ref.
The above-mentioned configuration controls the distance between the probe tip 106 and the sample 102 so that the distance is always kept to be constant. An XY scanning circuit 110 provides two output signals (Vx, Vy) to the X and Y actuators of the XYZ fine movement mechanism 104, respectively. The scanning signals (Vx, Vy) outputted from the XY scanning circuit 110 are used for causing the probe tip 106 to scan the surface of the sample 102 in the directions of the X-axis and the Y-axis. While the scanning operation is carried out, as mentioned above, the distance between the probe tip 106 and the sample 102 is maintained to be identical with the constant value set in advance.
Data Vz corresponding to the movement amount due to the Z actuator and data (Vx, Vy) as to output signals of the XY scanning circuit 110 are stored in a memory (not shown in the figure). As the result of carrying out necessary processing to these data, images as to the sample surface obtained by the measurement are displayed on a screen of a display unit 111. The shape of the surface in the sample 102 can be observed on the basis of the images. The atomic force microscope performing the measurement as mentioned above has very high measurement resolution, and in this microscope, further, when performing the measurement, a range for the measurement can be easily switched from a few nanometers scale to a few hundred micrometer scale.
In the aforementioned conventional AFM, the measurable range thereof is limited by that of the XYZ fine movement mechanism 104. It is essential for the XYZ fine movement mechanism 104 to use solid actuators formed by piezoelectric elements in order to make sure of the resolution of the atomic size level, as mentioned above. Consequently, the movable range of the conventional XYZ fine movement mechanism 104 sets a limit to about 100 .mu.m. Even if a stroke in the XYZ fine movement mechanism 104 is expanded in order to expand the movable range, its resolution is lowered. Therefore, it was general for the conventional AFM to set its scanning range as a fine range of about 10 .mu.m in view of a practical aspect.
On the other hand, in recent years, a request to measure a surface shape in a wide range, such as undulation on the surface of silicon wafers, by using a microscope with high measurement resolution no more than a nanometer level, like the AFM, is gradually increased. If the measurable range of the SPM having the high measurement resolution can be expanded in response to circumstances, value in use as the microscopes will be extremely raised.
Furthermore, there are many occasions that the use to combine the SPM utilizing the probe tip 106 with other different probes such as an ultrasonic microscope probe or a laser beam microscope probe, etc. is required. When making the complex configuration of the probe tip and a probe of another type, it is essential for the complex configuration to add a unit capable of expanding a scanning range, since the microscopes using the probe of another type have the low resolution in comparison with the AFM.